We propose a multidisciplinary research program that investigates the function of protein complexes at the heart of auditory reception in the model system, Drosophila melanogaster. The biology of hearing is astonishingly conserved between humans and fly: both the transcription factors that specify the development of organs of auditory reception and the molecular machines that transduce sound into neural signals are highly conserved. In both systems, cellular differentiation for the perception of sound requires elaborate subcellular arrangements of cytoskeletal elements, including actin filaments and microtubules. Mutations in the human and mouse orthologs of ck/myoVIIA and 10A/myoXV demonstrate the key roles these proteins play in auditory reception and vestibular function, but the molecular mechanism(s) by which these motor proteins contribute to these processes remain controversial. We propose an interdisciplinary approach to structure/function analysis of ck/myoVIIA, 28B/myoVIIB and 10A/myoXV (together, the myosin VII subfamily) in Drosophila where we use uniquely powerful molecular genetic tools to relate protein structure-function studies in vitro to structure/function analyses in vivo. We have already shown that ck/myoVIIA mutates to lethality, is required to drive changes in the structure of the actin cytoskeleton during morphogenesis and is required for auditory reception in adult flies. We have demonstrated that 10A/myoXV is essential for fly viability. We propose three specific aims 1) that address the cellular mechanisms of motor protein function;2) that identify the binding partners with which these motor proteins interact;and 3) elucidate the structure of their cargo binding tails. Our specific aims will inform one another, but do not depend on one another's success. Together, our studies offer unique opportunities to probe the supramolecular protein complexes that require motor protein function and that drive cellular function in auditory reception, vestibular function and morphogenesis.